Using a bunker for signing involves communication between three parties, the client, the relay, and the signer. So there are many possible points of failure, which makes it hard to debug. Thanks for your feedback, it will definitely help with the debugging.
Discussion
Yeah, that's why I watched for what I can observe and I saw that client to relay to signer did work but somehow signer to relay to client did not. But it's not a problem I can reproduce right now and it might have had to do with my machine sockets having been corrupted from suspending it.